30 THE PLIOCENE AND PLEISTOCENE DEPOSITS OF MARYLAND 



in 1860, he was more guarded in his statements. He thought them, 

 at least in part, post-Tertiary, and concluded that the materials out of 

 which they were built must have been transported from the north and 

 west. Seventeen years later W. B. Eogers referred to the gravel and 

 cobble-stone deposits of the Middle Atlantic States and added consider- 

 ably to the observations of earlier geologists, in that he recognized in these 

 surficial deposits about Eichmond, Washington, Baltimore, and Wil- 

 mington materials derived from the Paleozoic formations to the west. 

 He concluded that these were brought down by the present streams when 

 the land stood lower and the rivers were flooded toward their headwaters 

 by the melting ice of glaciers. He thus correlated these deposits with the 

 glacial period. 



The next year Stevenson referred to the terraces developed along the 

 river courses of western Maryland and suggested that they were cut at 

 about the time of the glacial epoch. Three years later, in 1881, Lewis, 

 working down into Marjdand from the north, recognized his Bryn Mawr 

 gravels on a hill near Elkton. Many of the hills which surround Elkton 

 are capped with Lafayette gravel, the equivalent of the Bryn Mawr, 

 while some are covered with younger deposits. As no name is given 

 to the particular hilltop on which the supposed Bryn Mawr gravels 

 were found, it cannot be determined at the present time whether Lewis 

 actually discovered Bryn Mawr gravels or whether he confused it with 

 one of the later deposits of the Columbia group. 



In 1884 and 1885 Chester of Delaware contributed two interesting 

 papers on the age and origin of the surficial formations. He divided 

 them into a high level or Bryn Mawr gravel which he considered as 

 possible Cretaceous, and Delaware gravels in which he recognized two 

 phases, the red sand and Philadelphia brick clay, which he considered 

 contemporaneous and of Quaternary age. Next he distinguished Estuary 

 sands which he also placed in the Quaternary and bog clay which he 

 believed to be " Modern." Most of Chester's remarks refer to the State 

 of Delaware, but he spent considerable time in studying the gravel deposits 

 as they are developed about the head of Chesapeake Bay in Maryland. 

 He concluded that the region must have been depressed at least 350 feet 



